I also had big problems with that one.
Without HD DVD it would not play at all under 3730a with full HDCP compliance.
PDVD just freezes (it's a PdVD bug, again!), as Arcsoft plays it (but does not support HDCP on my system, so this is as bad).

However, with updating AnyDVD on another HTPC hooked up with the internet I could play ID4 with PDVD 3104, but with heavy stuttering here and there (it's not the system, other BRs play just fine).

Yes, that's what I said, after I had the newest key downloaded, the BR played.

Question: During playback of a certain BR, is AnyDVD ever interacting with the process at all? Or is it only interacting at the start of the playback process?

Click to expand...

Anydvd just decrypts the disc when you first insert it in your drive. Anydvd doesn't start monkeying around with anything during playback (the exception, perhaps, being the use of HD-DVD scripts with Anydvd HD).